Soil carbon dioxide venting through rice roots

The growth of rice in submerged soils depends on its ability to form continuous gas channels—aerenchyma—through which oxygen (O2) diffuses from the shoots to aerate the roots. Less well understood is the extent to which aerenchyma permits venting of respiratory carbon dioxide (CO2) in the opposite d...

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Bibliographic Details
Published in:Plant, cell and environment cell and environment, 2019-12, Vol.42 (12), p.3197-3207
Main Authors: Kirk, Guy J.D., Boghi, Andrea, Affholder, Marie‐Cecile, Keyes, Samuel D., Heppell, James, Roose, Tiina
Format: Article
Language:English
Subjects:
Acidic soils
Aeration
Bicarbonates
biological models
biological transport
Carbon dioxide
Carbon Dioxide - metabolism
Carbon dioxide fixation
Carbon sequestration
Carbonic acid
Computed tomography
Mathematical models
Models, Biological
Nutrients
Original
Oryza - metabolism
Photosynthesis
Plant Roots - metabolism
Rhizosphere
Rice
Roots
Sensitivity analysis
Shoots
Soil - chemistry
Soil conditions
Soils
Toxicants
X‐ray computed tomography
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Summary:The growth of rice in submerged soils depends on its ability to form continuous gas channels—aerenchyma—through which oxygen (O2) diffuses from the shoots to aerate the roots. Less well understood is the extent to which aerenchyma permits venting of respiratory carbon dioxide (CO2) in the opposite direction. Large, potentially toxic concentrations of dissolved CO2 develop in submerged rice soils. We show using X‐ray computed tomography and image‐based mathematical modelling that CO2 venting through rice roots is far greater than thought hitherto. We found rates of venting equivalent to a third of the daily CO2 fixation in photosynthesis. Without this venting through the roots, the concentrations of CO2 and associated bicarbonate (HCO3−) in root cells would have been well above levels known to be toxic to roots. Removal of CO2 and hence carbonic acid (H2CO3) from the soil was sufficient to increase the pH in the rhizosphere close to the roots by 0.7 units, which is sufficient to solubilize or immobilize various nutrients and toxicants. A sensitivity analysis of the model showed that such changes are expected for a wide range of plant and soil conditions. Large, potentially toxic concentrations of dissolved CO2 accumulate in submerged paddy soils because CO2 from plant and soil respiration escapes only very slowly. We found, using X‐ray computed tomography and image‐based mathematical modelling, venting of soil CO2 through rice roots at rates equivalent to a third of the daily CO2 fixation in photosynthesis. Without this venting, the concentrations of CO2 and associated bicarbonate in root cells would have been well above levels known to be toxic to roots. Removal of soil CO2 and hence carbonic acid will also affect the solubility and hence plant uptake of various nutrients and toxicants in the rhizosphere.
ISSN:0140-7791
1365-3040
DOI:10.1111/pce.13638